If entrance to FOSDEM is free, who pays the expenses?

My company loves FOSDEM, what are the sponsoring possibilities?

I need a formal invitation for a VISA request

For legal reasons, the FOSDEM organization can only issue such
letters of invitation to "main track" speakers for whom we also make travel
and hotel arrangements.

If you are attending FOSDEM as part of your involvement with a project represented at our conference, we recommend you get in touch with someone you know locally who is involved in the project and ask them to invite you.